(1) Field of the Invention
The present invention relates to a toner cartridge and an image forming apparatus using this, in particular, relating to a toner cartridge used for an image forming apparatus for forming images with toner, such as an electrostatic copier, laser printer, facsimile machine and the like, as well as relating to an image forming apparatus using this toner cartridge.
(2) Description of the Prior Art
Conventionally, in image forming apparatuses using static electrophotography such as copiers, facsimile machines, etc., that use toner, toner is supplied to a developing device by a toner supply device with a toner cartridge or the like to perform continuous printout of images.
The image forming apparatus of this kind usually includes the steps of charging, exposure, development, transfer, separation, cleaning, charge erasing and fixing.
For example, in the process for forming images, the surface of a photoreceptor drum that is rotationally driven is uniformly electrified by a charging device (charging step), and the photoreceptor drum surface thus electrified is illuminated with a laser beam from an exposure device to form an electrostatic latent image (exposure step). Subsequently, the electrostatic latent image on the photoreceptor drum is developed by a developing device to form a toner image on the photoreceptor drum surface (developing step).
The toner image on the photoreceptor drum is then transferred to a transfer medium by a transfer device (transfer step), thereafter the transferred toner image is heated and fused to the transfer medium by a fusing device (fixing step).
On the other hand, the residual toner remaining on the photoreceptor drum surface after transfer is removed by a cleaning device and collected into a predetermined collecting portion (cleaning step). The photoreceptor drum surface after cleaning is cleared of residual charge by a charge erasing device to prepare for a next image forming operation (charge erasing step).
As the developer for developing the electrostatic latent image on the photoreceptor drum, a mono-component developer consisting of a toner only or a dual-component developer consisting of a toner and a carrier is usually used.
Since the mono-component developer does not include any carrier, there is no need to have an agitating mechanism for mixing and uniforming toner and carrier. Hence this developing device has the advantage of a simple structure. However, there is a drawback that the amount of static charge on the toner is unlikely to be stable.
On the other hand, since the dual-component developer needs to have an agitating mechanism for mixing the toner and carrier uniformly, there is a drawback that the developing device becomes complex. However, since the developer presents stability in the amount of charge and excellent suitability to high-speed machines, it is often used for high-speed image forming apparatuses and color image forming apparatuses.
The system for dual-component developer is arranged such that toner is supplied from the toner cartridge into the developing device when toner is consumed from the dual-component developer, so that the concentration of the toner in the developer in the developing hopper will not be lower than a predetermined level.
Recently, in order to meet the user demands for energy saving and high-quality printout of images, micro-sized toners having a low softening temperature with a volume mean diameter as low as 5 to 9 μm have become used. Though the toner of this kind is designed to be fixable at a low fixing temperature and is effective in enhancing resolution and reducing granulation to achieve improved image quality, the toner suffers from the problem that its fluidity is low, hence the toner is prone to clump together inside the toner cartridge.
As an example of a countermeasure against this toner clumping problem, there has been disclosed a toner cartridge which is adapted to perform reverse rotation for a fixed period of time when a new toner cartridge is mounted to the image forming apparatus in order to bring away the toner remaining around the toner discharge port from the toner discharge port (see patent document 1: Japanese Patent Application Laid-open 2002-162815).
It is true that this conventional method makes it possible to loosen the toner that was compacted before attachment of the toner cartridge to the image forming apparatus due to vibration etc., during transportation of the toner cartridge, for example, but once the toner has been compacted due to the lowering of fluidity of the toner under a high-temperature environment while the image forming apparatus is in operation after the toner cartridge was attached to the image forming apparatus, this method is not useful, resulting in failure to prevent the toner discharging screw from being locked.